The present invention generally relates to microwave integrated circuits, and more particularly, to a microwave integrated circuit for multiplexing radio frequency input signals that operates in an evanescent mode.
The conventional approach for achieving signal addition or subtraction of radio frequency (RF) signals is through the use of microstrip line multiplexers. The drawbacks of technology are their large overall size and low rejection frequency response. Typical dimensions of the reactive elements of microstrip line multiplexers are on the order of xcex/4, where xcex represents the wavelength of an RF signal of interest. Waveguide filters have been used at millimeter frequencies to provide sharp rejections, however, they are extremely large and heavy when they are used at low frequencies, i.e., less than 1 Ghz.
Multiband phased array systems may have hundreds to thousands of multiplexers in order to meet radiation and steering requirements. Integrated into each multiplexer are microwave integrated circuit (MIC) to process the signals for the phased array. Therefore, size and weight of the microwave integrated circuits are major factors of consideration in the design of phased array systems. Generally, multiplexers operate in the dominant mode so that the size of such devices depends on their frequency of operation.
Therefore, a need exists for a multiplexer that is small enough to be mounted on printed circuit boards, yet which still has the performance characteristics of larger waveguide multiplexers that operate in the dominant mode.
The present invention is an RF multiplexer than may be implemented using microwave integrated circuitry (MIC) technology to provide a multiplexer that operates with ultra-high Q evanescent mode in a metallized waveguide to perform RF signal distribution. Desired signals can operate at below the cut-off frequency of the dominant mode. Resonator elements may be fabricated using printed circuit fabrication techniques and embedded inside a low loss dielectrically loaded cavity that is coated with metallic materials. Respective inputs and outputs of the multiplexer in MIC format may be directly integrated with adjacent components on a printed circuit board. The invention enables high Q, small profile multiplexers to be effectively integrated with the active hardware of a communications system to provide low weight (LO) antenna systems. The invention also provides parallel signal multiplexing in a single housing and in real time. Additionally, the invention may be integrated on a single substrate with other communications components into a single, light weight structure.
An integrated circuit multiplexer embodying various features of the present invention comprises a waveguide having an interior cavity, first RF input port, and a first and second output ports; a dielectric structure positioned in the cavity; an RF input feed attached to the dielectric structure that extends through the RF input port; a first RF output feed attached to the dielectric structure that extends through the first RF output port; a second RF output feed attached to the dielectric structure that extends through the second RF output port; a first resonator pair mounted to the dielectric structure between the RF input feed and the first RF output feed, and electrically connected to the waveguide; and a second resonator pair mounted to the dielectric structure between the RF input feed and the second RF output feed, and electrically connected to the waveguide so that the first and second resonator pairs are generally coplanar. The waveguide is shaped as a right rectangular prism having a rectangular cross-sectional area characterized by a width L1 and a depth L2, where L1 less than (0.5)xcex, L2 less than (0.25)xcex, and xcex represents the center wavelength of a radio frequency signal that is input into said waveguide so that the waveguide operates in an evanescent mode in response to receiving the radio frequency signal.
These and other advantages of the invention will become more apparent upon review of the accompanying drawings and specification, including the claims.